1. Field of the Invention
Embodiments of invention generally relate to optical apparatus, methods, and applications thereof and, more particularly to optical apparatus including an optical resonant cavity combined with a wavelength demultiplexer, for e.g. but not limited to, resolution-enhanced spectrometers, light compositors, and wavelength-division multiplexing devices, and associated methods and applications.
2. Description of the Related Art
Several difficulties arise in the design of high resolution, wide range, and small footprint spectrometers. Designs such as etched diffraction gratings and arrayed waveguide gratings (AWGs) are limited in resolution by the number of grooves/waveguides. Since the size of the whole spectrometer needs to increase in order to accommodate more grooves/waveguides, the area of the device increases with the square of the resolution improvement. An AWG generally employs high order diffraction to improve its resolution, but since it comes with the cost of decreasing free spectral range (FSR) and thus decreasing spectral range available, this is not a particularly helpful solution.
Spectrometers employing an array of ring resonators have also been reported. In this case, high resolution with a small device area can be achieved, but due to fabrication limitations each ring resonator requires individual tuning, which increases the complexity of the system. Also, serial cascading of a very large number of ring resonators has the problem of optical attenuation since each ring has a finite insertion loss.
The inventors have thus recognized the benefits and advantages to be obtained from an optical apparatus such as, but not limited to, a spectrometer, having high resolution, wide spectral range, a small footprint, versatile materials platforms including CMOS assembly compatibility, that is suitable particularly but not solely for applications in chemical and biological sensing, optical metrology, and optical coherence tomography.